Chemical-mechanical polishing wafer and method of use

ABSTRACT

The present invention is directed to systems and methods for assisting personnel in discerning which side of a dummy wafer has been polished more and for differentiating one side of a dummy wafer from the other. In a preferred embodiment, dummy wafers include a first plurality of depth indicia on a first surface and a second plurality of depth indicia on a second opposing surface. In one embodiment, each of the depth indicia of the first plurality of depth indicia extends a depth into the dummy wafer beyond the first surface, and each of the depth indicia of the second plurality of depth indicia extends a depth into the dummy wafer beyond the second surface. Other embodiments include depth indicia of the first plurality of depth indicia located at depths beyond the first surface that each have a corresponding depth indicia in the second plurality of depth indicia located at a substantially similar depth beyond the second surface. In other embodiments, each of the depth indicia of the first and second pluralities of depth indicia are located at different depths.

TECHNICAL FIELD

This disclosure relates generally to wafers for use with chemical-mechanical polishing systems, and to such wafers including indicia in particular.

BACKGROUND

The present inventors have recognized that typical dummy wafers used in chemical-mechanical polishing operations, such as conditioning polishing pads, tend to be completely flat, smooth, and featureless on each side. The present inventors have also recognized that personnel operating chemical-mechanical polishing equipment commonly cannot distinguish one side of such a dummy wafer from the other, which commonly results in one side of the dummy wafer being used for polishing operations more frequently than the other. The present inventors have also recognized that such polishing of one side of a dummy wafer more frequently than the other typically causes such a wafer to warp or buckle, thus becoming unsuitable for use with chemical-mechanical polishing equipment despite there being material that could have been polished except for the warping or buckling.

Accordingly, the present inventors have recognized there is a need for a mechanism whereby personnel can readily discern which side of a dummy wafer has been polished more. The present inventors have also recognized a need for a mechanism to differentiate one side of a dummy wafer from the other.

SUMMARY

The present invention is directed to systems and methods for assisting personnel in discerning which side of a dummy wafer has been polished more and for differentiating one side of a dummy wafer from the other. In a preferred embodiment, dummy wafers include a first plurality of depth indicia on a first surface and a second plurality of depth indicia on a second opposing surface. In one embodiment, each of the depth indicia of the first plurality of depth indicia extends a depth into the dummy wafer beyond the first surface, and each of the depth indicia of the second plurality of depth indicia extends a depth into the dummy wafer beyond the second surface. Other embodiments include depth indicia of the first plurality of depth indicia located at depths beyond the first surface that each have a corresponding depth indicia in the second plurality of depth indicia located at a substantially similar depth beyond the second surface. In other embodiments, each of the depth indicia of the first and second pluralities of depth indicia are located at different depths.

In light of the above problems and needs recognized by the present inventors, this disclosure describes embodiments for an improved dummy wafer with depth indicia suitable for readily informing a chemical-mechanical polishing equipment operator which side of the dummy wafer has been polished more. This disclosure also describes embodiments for an improved dummy wafer with an indicia that differentiates one side of a dummy wafer from the other side of the dummy wafer.

Additional aspects and advantages will be apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a front plan view of an embodiment of a wafer bearing depth indicia.

FIG. 2 illustrates a left side view of the embodiment of FIG. 1.

FIG. 3 illustrates a detail view of a portion of FIG. 2.

FIG. 4 illustrates a detail view of a portion of FIG. 1.

FIG. 5 illustrates a back plan view of the embodiment of FIG. 1.

FIG. 6 illustrates a front plan view of the embodiment of FIG. 1 with some depth indicia worn away.

FIG. 7 illustrates a back plan view of the embodiment of FIG. 1 with some depth indicia worn away.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

While the following discussion references preferred embodiments having specific structures and markings, the invention is not limited to the particular details discussed. The described features, structures, characteristics, and methods may be combined in any suitable manner in one or more embodiments. In view of the disclosure herein, those skilled in the art will recognize that the various embodiments can be practiced without one or more of the specific details or with other methods, components, materials, or the like. In other instances, well-known structures, materials, or operations are not shown or not described in detail to avoid obscuring aspects of the embodiments. For convenience, the methods and systems may be described herein with reference to copper dummy wafers, however, it is understood that the details and methods described herein are applicable to any dummy wafer used for chemical-mechanical polishing.

Preferred embodiments of a dummy wafer 10 are illustrated in FIGS. 1-5. In the exemplary embodiment illustrated in FIGS. 1-5, dummy wafer 10 includes an optional side indicia 15, a first plurality of depth indicia 20, and a second plurality of depth indicia 40. A purpose for the first plurality of depth indicia 20 and the second plurality of depth indicia 40 is to permit a chemical-mechanical polishing equipment operator to readily discern which surface of the dummy wafer 10 has been polished more, as described below. Dummy wafer 10 is preferably made from copper, for example from copper sheeting that is approximately 0.0315 of an inch thick, and includes chamfers 11. Dummy wafer 10 may be made from other suitable materials, such as silicon for example.

Dummy wafer 10 includes a first surface 12 and a second, opposing surface 13 that are suitably flat for chemical-mechanical polishing operations. For example, in one embodiment first surface 12 and second surface 13 have a flatness with a tolerance between approximately 0.0100 of an inch and approximately 0.0040 of an inch. Preferably, first surface 12 and second surface 13 have a flatness with a tolerance of approximately 0.0078 of an inch, or less.

The first plurality of depth indicia 20 include 10 separate indicia 21, 22, 23, 24, 25, 26, 27, 28, 29, and 30. The second plurality of depth indicia 40 include 10 separate indicia 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50. However, any suitable number of indicia may be used for the first and second pluralities of indicia 20 and 40, preferably two or more. In other embodiments, the number of indicia in the first plurality of indicia does not equal the number of indicia in the second plurality of indicia.

FIG. 1 illustrates the front side indicia 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 and FIG. 5 illustrates the rear side indicia 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50 as numerals. However, any suitable markings may be used for the indicia 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50, for example, geometric shapes, images, letters, collections of dots, etc., may be used.

Each of indicia 21, 22, 23, 24, 25, 26, 27, 28, 29, and 30 extend a depth below first surface 12. Each of indicia 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50 extend a depth below second surface 13. In a preferred arrangement, each of the indicia 21, 22, 23, 24, 25, 26, 27, 28, 29, and 30 of the first plurality of indicia 20 extend a different depth below the surface 12. Likewise, each of the indicia 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50 extend a different depth below the surface 13 in a preferred arrangement.

In a preferred embodiment, front indicia 21, 22, 23, 24, 25, 26, 27, 28, 29, and 30 of the first plurality of indicia 20 have a corresponding rear indicia 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50 of the second plurality of indicia 40. In other words, the marking forming front indicia 21 is substantially identical to the marking forming rear indicia 41, and the depth front indicia 21 extends below surface 12 is substantially identical to the depth rear indicia 41 extends below surface 13, and so on for each pair of indicia 22/42, 23/43, 24/44, 25/45, 26/46, 27/47, 28/48, 29/49, and 30/50. For example, indicia 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50 may be numerals as illustrated in FIGS. 1 and 5. And, each pair of indicia 21/31, 22/42, 23/43, 24/44, 25/45, 26/46, 27/47, 28/48, 29/49, and 30/50 may have an increasing, or graduated depth, for example, by extending approximately 0.0004 of an inch, approximately 0.0008 of an inch, approximately 0.0012 of an inch, approximately 0.0016 of an inch, approximately 0.0020 of an inch, approximately 0.0024 of an inch, approximately 0.0028 of an inch, approximately 0.0032 of an inch, approximately 0.0036 of an inch, and approximately 0.0040 of an inch below the first surface 12 and second surface 13, respectively. A preferred tolerance for such depths is +0.0005 of an inch deeper and −0.0 of an inch shallower. Other suitable depths may be used.

In other embodiments, the marking forming front indicia 21 is substantially identical to the marking forming rear indicia 41, but the depth front indicia 21 extends below surface 12 is different from the depth rear indicia 41 extends below surface 13, and so on for each pair of front and rear indicia 22/42, 23/43, 24/44, 25/45, 26/46, 27/47, 28/48, 29/49, and 30/50. For example, indicia 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50 may be numerals as illustrated in FIGS. 1 and 5. And, each pair of indicia 21/31, 22/42, 23/43, 24/44, 25/45, 26/46, 27/47, 28/48, 29/49, and 30/50 may extend approximately 0.0004 of an inch/0.0002 of an inch, approximately 0.0008 of an inch/0.0006 of an inch, approximately 0.0012 of an inch/0.0010 of an inch, approximately 0.0016 of an inch/0.0014 of an inch, approximately 0.0020 of an inch/0.0018 of an inch, approximately 0.0024 of an inch/0.0022 of an inch, approximately 0.0028 of an inch/0.0026 of an inch, approximately 0.0032 of an inch/0.0030 of an inch, approximately 0.0036 of an inch/0.0034 of an inch, and approximately 0.0040 of an inch/0.0038 of an inch below the first surface 12 and second surface 13, respectively. Other suitable depths may be used.

In another embodiment, side indicia 15 is included. Side indicia 15 may be located on the first surface 12 or the second surface 13. Side indicia 15 preferably extends a depth into wafer 10 that is greater than the depth of any of the first plurality of depth indicia 20 and of the second plurality of depth indicia 40. For example, side indicia 15 may extend 0.0045 of an inch below the first surface 12. Other suitable depths may be used. One purpose of including side indicia 15 is to permit an operator of chemical-mechanical polishing equipment to readily discern surface 12 from surface 13. In other embodiments, the marking used to form indicia 21, 22, 23, 24, 25, 26, 27, 28, 29, and 30 are different from the markings used to form indicia 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50. Thus, indicia 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50 may also serve as a side indicia.

The first plurality of depth indicia 20, second plurality of depth indicia 40, and side indicia 15, if present, are preferably machined into wafer 10. For example, a milling machine is preferably used to cut indicia 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50 and/or side indicia 15 into the first and second surfaces 12 and 13. Exemplary indicia 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50 include 18 point numerals made using a Century Gothic font. An exemplary side indicia 15 includes markings made using a 14 point Times New Roman font. Other suitable manners, such as etching OT laser ablation, may be used to form the first plurality of depth indicia 20, the second plurality of depth indicia 40, and/or the side indicia 15.

The first plurality of depth indicia 20 and the second plurality of depth indicia 40 may be arranged along an arc, as illustrated in FIGS. 1 and 5. In other embodiments, the first plurality of depth indicia 20 and the second plurality of depth indicia 40 are arranged along other geometric shapes, or portions of geometric shapes, or they may be placed randomly on the first surface 12 and the second surface 13. The relative location of indicia in the first plurality of depth indicia 20 on the first surface 12 and the relative location of indicia in the second plurality of depth indicia 40 on the second surface 12 may, or may not, correlate.

When a wafer, such as wafer 10, is used for chemical-mechanical polishing operations, a new wafer is polished until the shallowest of the depth indicia of either the first or second pluralities of depth indicia 20/40 is removed. Such polishing may occur after several polishing operations, or during the same polishing operation. When a chemical-mechanical polishing equipment operator observes that the shallowest indicia of either the first plurality or of the second plurality of depth indicia 20/40 has been removed, the wafer 10 is loaded, or re-loaded, into the chemical-mechanical polishing equipment so that the surface containing the shallowest indicia is being polished.

For example, during a test of the durability of a polishing pad, a new wafer 10 is loaded into a chemical-mechanical polisher with surface 12 facing up, i.e., being polished. As polishing proceeds and material is removed from the surface 12, indicia 21 eventually disappears. The operator stops the chemical-mechanical polisher and flips wafer 10 so surface 13 now faces up. As polishing proceeds and material is removed from the surface 13, indicia 41 eventually disappears. The operator again stops the chemical-mechanical polisher and flips wafer 10. By monitoring the amount of material removed from surfaces 12 and 13 by watching for the alternating disappearance of front/rear indicia pairs 21/41, 22/42, 23/43, 24/44, 25/45, 26/46, 27/47, 28/48, 29/49, and 30/50 as wafer 10 is flipped, the useful life of wafer 10 is preferably extended when compared to wafers that do not bear indicia, such as front indicia 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 and rear indicia 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50. Preferably, such useful life extension occurs by balancing the amount of stresses created on surfaces 12 and 13 to prevent one side from expanding or contracting more than the other to a degree that warps, buckles, or cracks wafer 10, thus making it unsuitable for use in the chemical-mechanical polishing equipment.

Wafer 10 does not need to be polished in one continuous polishing procedure to realize benefits from including the first plurality of depth indicia 20 and the second plurality of depth indicia 40. For example, the present inventors have recognized that without depth indicia, over the course of multiple polishing operations it is difficult or cumbersome to track which side of a wafer has received more polishing (and thus incurred more material loss and higher stresses). Accordingly, the present inventors have recognized that wafers may be placed into chemical-polishing equipment such that the surface that has received the greatest amount of polishing is facing up. The present inventors have also recognized that over-polishing one surface over the other leads to residual stress build-up that warps, distorts, or cracks the wafer and lessens the useful life of such a wafer. By including a first plurality of depth indicia 20 and a second plurality of depth indicia 40, embodiments permit chemical-mechanical polishing equipment operators to readily discern which surface has received the most polishing merely by comparing the first plurality of depth indicia 20 against the second plurality of depth indicia 40. Knowing which surface has received the lesser amount of polishing permits the operator to place that side up for the next polishing operation.

For example, an operator may perform a method of using a wafer 10 for chemical-mechanical polishing, comprising performing a polishing operation using the wafer 10. The operator then returns the wafer 10 to a storage area. The operator retrieves the wafer 10 from the storage area and checks the first plurality of depth indicia 20A (FIG. 6) borne on the first surface 12 of the wafer 10 as well as the second plurality of depth indicia 40A (FIG. 7) borne on the second surface 13 of the wafer 10. The operator determines whether the first surface 12 or the second surface 13 should be polished based on checking the first and second pluralities of depth indicia 20A and 40A. For example, the operator notes the lowest numeral appearing on surface 12 and the lowest numeral appearing on surface 13. The surface with the lowest numeral showing is chosen to be polished. If the lowest numeral is the same for both surfaces 12 and 13, then there is no preference for which surface is polished. The operator then performs a polishing operation on the determined first or second surface (in the illustrated instance of FIGS. 6 and 7, surface 12 is chosen).

In another exemplary method for using a wafer in chemical-mechanical polishing, a wafer having first and second front side indicia on a front surface and first and second rear side indicia on a rear surface is provided. The first and second front side indicia both extend below the front surface, and the second front side indicia extends further below the front surface than the first front side indicia, i.e., the second front side indicia has a greater depth than the first front side indicia. Likewise, the first and second rear side indicia both extend below the rear surface, and the second rear side indicia extends further below the rear surface than the first rear side indicia, i.e., the second rear side indicia has a greater depth than the first rear side indicia. An amount of polishing for the front surface is determined by inspecting the first and second front side indicia. An amount of polishing for the rear surface is determined by inspecting the first and second rear side indicia. Based on the amount of polishing determinations made for the front and rear surfaces, whichever of the front or rear surface has been polished less is chosen for polishing.

It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by the following claims. 

1. A wafer for chemical-mechanical polishing comprising: a substrate having a first flat surface, a second flat surface opposing the first flat surface, and a thickness defined between the first and second flat surfaces, wherein each of the first and second flat surfaces exhibit a flatness with a tolerance between approximately 0.0100 of an inch and approximately 0.0040 of an inch, a first depth indicia borne on the first flat surface, wherein the first depth indicia extends a first depth below the first flat surface; a second depth indicia borne on the first flat surface, wherein the second depth indicia extends a second depth below the first flat surface and the second depth is greater than the first depth; a third depth indicia borne on the second flat surface, wherein the third depth indicia extends a third depth below the second flat surface; a fourth depth indicia borne on the second flat surface, wherein the fourth depth indicia extends a fourth depth below the second flat surface and the fourth depth is greater than the third depth.
 2. A wafer according to claim 1, further comprising a side indicia borne on the first flat surface, wherein the side indicia extends a fifth depth below the first flat surface; wherein the first depth is less than the fifth depth; wherein the second depth is equal to or less than the fifth depth; wherein the third depth is less than the fifth depth; and wherein the fourth depth is equal to or less than the fifth depth.
 3. A wafer according to claim 1, wherein the wafer is made of copper.
 4. A wafer according to claim 1, wherein the first depth is substantially equal to the third depth.
 5. A wafer according to claim 4, wherein the second depth is substantially equal to the fourth depth.
 6. A wafer according to claim 1, wherein: the first depth is approximately 0.0004 of an inch; the second depth is approximately 0.0008 of an inch; the third depth is approximately 0.0004 of an inch; and the fourth depth is approximately 0.0008 of an inch.
 7. A wafer according to claim 1, wherein: the first depth is approximately 0.0004 of an inch; the second depth is approximately 0.0008 of an inch; the third depth is approximately 0.0002 of an inch; and the fourth depth is approximately 0.0006 of an inch.
 8. A wafer according to claim 1, wherein: the first depth indicia is substantially identical to the third depth indicia; and the second depth indicia is substantially identical to the fourth depth indicia.
 9. A wafer according to claim 1, wherein the thickness is approximately 0.0315 of an inch.
 10. A wafer according to claim 1, wherein: the first depth indicia borne on the first flat surface is configured to be worn away via polishing before the second depth indicia borne on the first flat surface to indicate a first amount of polishing; the third depth indicia borne on the second flat surface is configured to be worn away via polishing before the fourth depth indicia borne on the second flat surface to indicate a second amount of polishing; the second depth indicia borne on the first flat surface is configured to be worn away via polishing to indicate a third amount of polishing; and the fourth depth indicia borne on the second flat surface is configured to be worn away via polishing to indicate a fourth amount of polishing.
 11. A wafer for chemical-mechanical polishing comprising: a substrate having a first flat surface, a second flat surface opposing the first flat surface, and a thickness defined between the first and second flat surfaces, wherein each of the first and second flat surfaces exhibit a flatness with a tolerance between approximately 0.0100 of an inch and approximately 0.0040 of an inch, a first plurality of depth indicia borne on the first flat surface, wherein each of the first plurality of depth indicia extends a depth below the first flat surface, wherein no two of the first plurality of depth indicia extend the same depth below the first flat surface; and a second plurality of depth indicia borne on the second flat surface, wherein each of the second plurality of depth indicia extends a depth below the second flat surface, wherein no two of the second plurality of depth indicia extend the same depth below the second flat surface.
 12. A wafer according to claim 11, wherein the depth for each of the first plurality of depth indicia has a corresponding approximately equal depth in the depths for the second plurality of depth indicia.
 13. A wafer according to claim 12, wherein: a first indicia for the first plurality of depth indicia extends approximately 0.0004 of an inch below the first surface, and each subsequent indicia for the first plurality of depth indicia extends approximately an additional 0.0004 of an inch below the first surface; and a first indicia for the second plurality of depth indicia extends approximately 0.0004 of an inch below the second surface, and each subsequent indicia for the second plurality of depth indicia extends approximately an additional 0.0004 of an inch below the second surface.
 14. A wafer according to claim 11, wherein: each depth for the first plurality of depth indicia is different from each depth for the second plurality of depth indicia.
 15. A wafer according to claim 14, wherein: a first indicia for the first plurality of depth indicia extends approximately 0.0004 of an inch below the first surface, and each subsequent indicia for the first plurality of depth indicia extends approximately an additional 0.0004 of an inch below the first surface; and a first indicia for the second plurality of depth indicia extends approximately 0.0002 of an inch below the second surface, and each subsequent indicia for the second plurality of depth indicia extends approximately an additional 0.0004 of an inch below the second surface.
 16. A wafer according to claim 11, wherein the wafer is made of copper.
 17. A wafer according to claim 11, further comprising a side indicia borne on the first flat surface, wherein the side indicia extends a depth below the first flat surface that is greater than a maximum depth for an indicia of the first plurality of depth indicia.
 18. A wafer for chemical-mechanical polishing comprising: a substrate means having a first flat surface and a second flat surface for being chemically-mechanically polished; a first depth indicating means for indicating an amount of wear occurring on the first surface; and a second depth indicating means for indicating an amount of wear occurring on the second surface.
 19. A wafer according to claim 18, further comprising: a side indicating means for differentiating the first flat surface from the second flat surface. 